@parimbi : GPGMail 2.0 is for 10.7 only so far. We might do a backport later, but are currently busy getting it stable for 10.7 Lion. You can always find old versions for old 10.x systems on the webpage: http://www.gpgtools.org/gpgmail/index.html

Excellent plug-in (or bundle in correct nomenclature) for Mail.app. Does exactly what it's meant to do, and does it with stability and efficiency. Will show icons in the header section whether the email is signed or encrypted or both, and really feels like it's a part of the application.